The present invention relates to the detection and analysis of target nucleotide sequences associated with cancer. The invention provides novel microRNAs, oligonucleotide probes which can detect the novel microRNAs, and methods employing the use of oligonucleotide probes that are useful for detecting and analysing target nucleotide sequences associated with cancer.
MicroRNAs (miRNAs) have rapidly emerged as an important class of short endogenous RNAs that act as post-transcriptional regulators of gene expression by base-pairing with their target mRNAs. The 19-25 nucleotide (nt) mature miRNAs are processed sequentially from longer hairpin transcripts by the RNAse III ribonucleases Drosha (Lee, Y., et al., 2003. Nature 425: 415-419.) and Dicer (Hutvagner, G., et al., 2001. Science 293: 834-838, Ketting, R. F., et al., 2001. Genes Dev. 15: 2654-2659.). To date more than 3400 microRNAs have been annotated in vertebrates, invertebrates and plants according to the miRBase database release 7.1 in October 2005 (Griffiths-Jones, S. 2004. NAR 32 (Database issue), D109-D111), and many miRNAs that correspond to putative genes have also been identified. Some miRNAs have multiple loci in the genome (Reinhart, B. J., et al., 2002. Genes Dev. 16, 1616-1626.) and occasionally, several miRNA genes are arranged in tandem clusters (Lagos-Quintana, M., et al., 2001. Science 294: 853-858.). Recent bioinformatic predictions combined with array analyses, small RNA cloning and Northern blot validation indicate that the total number of miRNAs in vertebrate genomes is significantly higher than previously estimated and maybe as many as 1000 (Bentwich, I., et al., 2005. Nat. Genet. 37: 766-770, Berezikov, E., et al., 2005. Cell 120: 21-24, Xie, X., Lu, J., et al., 2005. Nature 434: 338-345.).
In a series of publications during recent years, it has become clear that microRNAs are extensively involved in cancer pathogenesis, and microRNA has been shown to be differentially expressed in a number of cancers (Breast cancer: Iorio et al Cancer Res 2005; 65: 7065. Lung cancer: Yanaihara et al Cell Science 2006; 9: 189-198. Chronic lymphocytic leukaemia (CLL): Galin et al PNAS, 2004 101(32):11755-11760. Colon cancer: Cummins et al PNAS 2006, 103 (10):3687-3692. Prostate cancer: Volinia et al PNAS 2006; 103: 2257). In fact, in a landmark paper Lu et al (Nature 2005; 435:834-838) demonstrated that differential expression of microRNA in multiple cancers types, and that signatures based on approximately 200 microRNAs improve classification of poorly differentiated cancers over mRNA profiles.
Furthermore, the expected complexity of the “microRNA'nome” is far smaller than the human transcriptome with the total number of microRNAs being approximately limited to between 800 to 1000. Therefore, a microRNA cancer signature can be predicted to include from 5-20 microRNAs, suggesting that microRNA based theranostics will be of limited complexity and far more robust than mRNA profiles.
Taken together microRNA constitutes a new class of non-coding RNAs that plays a significant role in determining gene expression, microRNAs are differentially expressed in human cancers and a series of recent publication show that microRNA classify human cancers; in some cases improvement over mRNA classification is observed.
The present invention allows for the determination of microRNA signatures that improve the classification of early diagnosed cancers. The microRNA signatures—following from the role of microRNAs in cancer—reveal the true cancerous potential of the tumor, and enable physicians to select the appropriate treatment. microRNA based cancer classification may significantly benefit patient care, because recurrence rate may be improved due to adequate treatment of traditionally classified low risk patients, and suitable therapy, such as adjuvant chemotherapy for breast cancer may be deselected for the large group of patients that do not benefit from it.
PCT/DK2005/000838, and U.S. application Ser. No. 11/324,177, both hereby incorporated by reference, discloses methods for the detection of microRNAs (miRNAs) using oligonucleotides which comprise nucleotide analogues, such as locked nucleic acids (LNAs).
WO2005/098029, hereby incorporated by reference, discloses a method using oligonucleotides for the detection, quantification, monitoring of expression of siRNA and/or miRNA. It is suggested that the method can be used for determining the differences between nucleic acid samples from e.g. a cancer patient.
The Sanger Institute publishes known miRNA sequences in the miRBase database (http://microrna.sanger.ac.uk/seauences/index.shtml). To date there are 533 human siRNAs present in the miRBase database.
WO2006/015312 discloses sets of genetic markers which can be correlated with a prognosis of breast cancer.
Iorio et al, (Cancer Res 2005; 65 (16), pp 7065-7070) discloses miRNAs whose expression profile is altered between breast cancer tumors and non tumor cells.